An international publication No. WO 2009/020087 discloses an example of the double-row roller bearing, which is composed of an outer ring whose inside circular surface has two rows of outside grooved tracks, or races, extending circumferentially of the outer ring, an inner ring whose inside circular surface has two rows of inside grooved races extending circumferentially of the inner ring in opposition to the outside grooved races of the outer ring to define raceways between the outside grooved races and inside grooved races, and a plurality of rollers lying in the raceways so as to circulate through the raceways with carrying loads as the inner ring and the outer ring rotate relative to each other. With the outside and inside grooved races, the race surfaces on which the rollers roll through intersect with skew regulator surfaces to form a substantially V-shape in a transverse cross-section. The skew regulator surfaces face to axially opposite ends of the rollers with leaving minute clearances between them. On the skew regulator surfaces on the outside grooved races, moreover, there are each provided a circular ridge flanked by annular recesses extending circumferentially of the inside circular surface of the outer ring, the circular ridge lying in opposition to a rotation axis of the roller. On the skew regulator surfaces on the inside grooved races, there are each provided a circular ridge flanked by annular recesses extending circumferentially of the outside circular surface of the inner ring, the circular ridge lying in opposition to a rotating axis of the roller. Furthermore, the outer ring has passages extending radially from the floors of the outside grooved races to release lubricant.
Of some commonly-assigned Japanese patent applications concerned with roller bearings, the commonly-assigned Japanese Laid-Open Patent Application 2000-314 418 discloses an angular-contact roller bearing constructed as shown in FIGS. 15 and 16 to make assemblage as well as downsizing easier. With the prior angular-contact roller bearing as shown in FIG. 15, two rows of raceways 60 are formed between an outer ring 51 and an inner ring 52, and the rollers 53 are disposed in the raceways 60 in such a fashion that their rotation axes are tilted or askew with respect to a rotating shaft to support the outer ring 51 and the inner ring 52 for rotation. The outer ring 51 has a loading hole 55 to charge the rollers 53 into the raceways 60 through there. The loading hole 55 is closed with a plug 67 after the completion of introduction of the rollers 53 into the raceways 60. With an inside circular surface 58 of the outer ring 51, there is no difference or gap in level on opposite sides of the outside grooved race 56. With an outside circular surface 59 of the inner ring 52 as well, there is no difference or gap in level on opposite sides of the inside grooved race 57. Both the outside grooved race 56 and the inside grooved race 57 have a V-shape in a transverse cross-section, whose one sides are race surfaces 63 and 65 coming into rolling contact with the circular rolling surfaces 61 of the rollers 53 and whose the other sides are guide surfaces 64 and 66 born against the axially opposite ends 62 of the rollers 53. The race surfaces 63 and 65 and the guide surfaces 64 and 66 are made identical in configuration with each other. The angular-contact roller bearing constructed as stated earlier, moreover, has separators 54 each of which is interposed between any adjacent rollers 53 lying between the grooved races 56 and 57 (refer to FIG. 16). The separator 54 as shown in FIG. 16 includes an upper surface 68 and lower surface 69 lying in opposition to race surfaces 63 and 68 of the races, along which the rollers 53 roll through, with leaving slight clearances to keep the upper and lower surfaces 68, 69 apart from the race surfaces 63 and 68, a major column 70 joining the upper and lower surfaces 68 and 69 together, and edge surfaces lying in opposition to guide surfaces of the races, against which the axially opposite ends 62 of the rollers 53 are opposed, with leaving slight clearances to keep the edge surfaces apart from the guide surfaces. The separator 54 has leading and trailing major sides concaved in symmetry with each other to fit over the rollers 53. Moreover, the concaved surfaces on the major sides are contoured in arced or curved profiles that the concaved sides bulge or rise gradually as their concavities get closer towards the centers thereof, so that the rollers 53 are guided while turning, with coming into touch with only the bulged centers in the concaved sides of the separator 54.
Another prior double-row turning bearing as shown in FIG. 17 is described in Japanese Laid-Open Patent Application No. 2002-13 540, in which a plurality of rolling elements of rollers 73 is installed in double rows of raceways 74 defined between an outer ring 71 and an inner ring 72. Especially, the prior double-row turning bearing is composed of the outer ring 71 having an inside circular surface on which double rows of grooved races 75 are formed to extend circumferentially of the inside circular surface, the inner ring 72 placed inside the outer ring 71 and having an outside circular surface on which double rows of grooved races 76 are formed to oppose circumferentially to the grooved races 75 on the outer ring 71, and a plurality of rolling elements 73 installed in double rows of the raceways 74 defined between the grooved races on the outer ring and the inner ring. Either of the outer ring 71 and the inner ring 72 has a loading hole 77 on each raceway 74, which extends radially of the ring to make it possible to charge the rolling elements 73 into the raceway 74.
Meanwhile, with the prior double-row roller bearing, there have been made a relief side at a location where the race surface and the guide part for the axially opposite ends of the roller merge or meet with each other in the grooved race. The relief side usually has a width necessary to precisely finish the race surface and the guide surface into the desired profiles. With the prior double-row roller bearing, moreover, there is no difference in level across the overall width of the bearing in both the outside circular surface on the inner ring and the inside circular surface on the outer ring. Thus, for the foregoing constructional reasons, the circumferential grooves are made on widthwise opposite sides of the bearing to form the skew regulator surfaces for the provision of the guide parts born against the axially opposite ends of the roller. On grinding work to cut the grooved races, abrasive grains broken up from the grinding wheel are released towards the relief sides. Even though the cutting edge of the grinding wheel becomes the slightly dull or loaded surface out of the desired profile, there is left no debris on the race surfaces of the grooved races and therefore, the grooved races are made precisely in the desired profile thanks to the relief sides. With the conventional double-row roller bearings, since the relief sides are made not only in the guide surfaces but also in the race surfaces, the effective contact length on the race surfaces of the outer ring and the inner ring are made less compared with the effective contact length on the circular rolling surface of the roller. Thus, it remains a major challenge that the prior double-row roller bearing is lowered in the load-carrying capacity. Moreover, the guide surface in the inner ring is made to come into a sliding contact with the axially opposite ends of the roller across the overall widthwise dimension in the diametral direction of the axially opposite ends of the roller. As a result, the guide surface in the prior double-row roller bearing poses a serious problem in which the contact area in the axially opposite ends of the roller becomes large and therefore causes big frictional resistance.